Isospecific polymerizations of alkyl methacrylates with a bis(alkyl)Yb complex and formation of stereocomplexes with syndiotactic poly(alkyl methacrylate)s

Yb[C(SiMe3)3]2 initiates the living polymerization of methyl methacrylate (MMA) at −78°C to give the polymer with Mn of 51.0×104 (Mw/Mn=1.1) and high isotacticity (97%) in a quantitative yield. Mixing of the acetone solution of resulting polymer (Mn=16.3×104) with the acetone solution of syndiotactic poly(MMA) (Mn=15.7×104) prepared by the (C5Me5)2SmMe(THF) initiator produces desired stereocomplex in high yield bearing very high Tm whose tensile modulus is higher than the respective isotactic and syndiotactic poly(MMA)s. Yb[C(SiMe3)3]2 also generated isotactic (98%) poly[2-(dimethylamino)ethyl methacrylate] (DMEMA), and (C5Me5)2SmMe(THF) affords the syndiotactic (97%) polymer in high yields. The combination of isotactic poly(MMA)-block-poly(DMEMA) (97/3) and syndiotactic poly(MMA)-block-poly(DMEMA) (97/3) provides the amphiphathic stereocomplex. In sharp contrast to the catalysis of Yb[C(SiMe3)3]2 in toluene, the addition of THF or HMPA resulted in the formation of syndio-rich poly(MMA).